At present, a oil chromatography detection device of transformer mainly adopts overall design of machine cabinet pattern. That is, all valve body and electrical elements of the oil chromatographic detection device are arranged in the machine cabinet according to structure of the machine cabinet. This design has complex structure and poor capacity of resisting disturbance, demands for a lot of extra resources allocated, wastes resources, demands for large space occupied and is inconvenience in maintenance and installation. Chinese utility model patent document CN201425590Y discloses a vacuum degasser used in online chromatographic analysis for oil of transformer. The vacuum degasser comprises an oil pump, an oil cylinder, a gas cylinder, a deaeration cavity, a mixer motor, and a plenum cavity which is a six-way valve and sample loop. Firstly, by action of the oil cylinder towards one side of the oil cylinder with an oil cylinder rod, the deaeration cavity is expanded, which drives oil in the deaeration cavity flowing into the oil cylinder (a section of the oil cylinder into which the oil flows is called cavity of the oil cylinder) to lower oil level. Then the oil in the deaeration cavity is stirred by a stirrer driven by the mixer motor, which leads to dissolved gas evolving from the oil and realizing new equilibrium of oil and gas. By action of the oil cylinder towards the other side of the oil cylinder without the oil cylinder rod, most of the evolved gas is pushed into the plenum cavity. Then the passage between the deaeration cavity and the plenum cavity is closed. By action of the gas cylinder towards a side of the gas cylinder with gas cylinder rod, evolved gas retained in the passage is pushed into the plenum cavity. So gas transfer and compression is implemented. Gas preserved in the plenum cavity is available for injection analysis of the online chromatographic analysis. However, oil-gas separation achieved by means of stirring takes more time and has poor effect. And due to using the mixer motor and the deaeration cavity, an oil-gas separation device is complex in structure and takes large space.